[0001] This invention is directed to the field as semiconductor processing, and more particularly,
to a novel multiple-processing and contamination-free plasma etching system.
[0002] Plasma etching devices are commonly employed during one or more of the phases of
the integrated circuit fabrication process, and are typically available in either
a single-wafer or a plural-wafer configuration. The single-wafer configurations, while
providing excellent process control, suffer from a restricted system throughput capability.
Efforts to relieve the throughput limitations, have been generally unsuccessful. For
these high-temperature etching processes, system utility is limited due to the undesirable
phenomenon of resist "popping", notwithstanding that various cooling approaches have
been used including clamping, cooling of the wafer underside with a helium flow, and
the mixing of helium into the plasma. The multiple-wafer configuration, while providing
a comparatively much-greater system throughput, have been generally subject to less-than-desirable
process and quality control. Not only are end-point determinations for each of the
multiple wafers either not available or not precisely determinable, but also electrode
positional accuracy for different electrode gaps and correspondingly different gas
chemistries is often difficult to establish and maintain. The single-wafer and the
multiple-wafer configurations are both subject to the further disadvantage that two
or more step processes typically expose the wafers to an undesirable environment in
the intermediate handling step, which materially increases the possibility of wafer
contamination, and which further restricts the processing throughput.
[0003] The present invention contemplates plural single-wafer plasma reactors each operative
inidividually to provide excellent process control of single wafers, collectively
operative to provide a system throughput limited only by the number of the plural
plasma reactors, and so cooperative with a common wafer transfer and queuing means
as to provide both single-step and multiple-step wafer processing in a manner that
neither exposes the wafers to an undesirable atmosphere not to human handling.
[0004] In the preferred embodiment, plural plasma reactors and cassettte elevator are symmetrically
arrayed about an X, TT movable wafer arm assembly. The plural reactors, the cassette
elevator, and the X, TT movable wafer arm are maintained in a controlled vacuum condition,
and the central S, TT movable wafer arm is in radial communication with the peripherally
surrounding plasma reactors and cassette elevator via a corresponding one of a plurality
of vacuum lock valves. The arm of the R, TT movable wafer arm assembly includes an
apertured platform for supporting each wafer, and a cooperative bumper for releasably
engaging the back and the periphery of the supported wafer without any wafer front
surface contact. Plural wafer contact responsive sensors mounted to the platform are
operative to provide a signal indication of whether or not the wafer is in a properly
seated condition. Each of the plural plasma reactors includes a stationary bottom
electrode and a movable upper electrode that are cooperative to provide a variable
wafer-cathode to anode gap therebetween of a selectable dimension. In one embodiment,
a support assembly including a micrometer adjustment stop is provided for selectively
positioning the movable electrode, and in another embodiment, a combination micrometer
stop and pneumatic actuators are provided for selectively positioning the movable
electrode. A vertically movable pedestal is slidably mounted centrally to the stationary
electrode of each of the plural plasma reactors that cooperates with the apertured
platform of the R, TT movable wafer arm assembly to load and unload the wafers respectively
onto and off of the stationary electrode. A reactant gas injection system, a RF power
source, and an end-point determination means are operatively coupled to each of the
plural plasma reactors. The plural plasma reactors are operable in either embodiment
to run the same or different processes, and are cooperative with the R, TT movable
wafer arm assembly to provide one of the same single-step processing simultaneously
in the plural plasma reactors, different single-step processing simultaneously in
the plural plasma reactors, and sequential two or more step processing in the plural
reactors. Two embodiments of the R, TT movable wafer arm assembly are disclosed.
[0005] These are other features, and advantages, of the present invention will become apparent
as the invention becomes better understood by referring to the following solely-exemplary
and non-limiting detailed description of the preferred embodiments thereof, and to
the drawings, wherein:
Figure 1 is a pictorial diagram illustrating the multiple-processing and contamination-free
plasma etching system according to the present invention;
Figure 2 is a fragmentary plan view, partially broken away, of the multiple-processing
and contamination-free plasma etching system according to the present invention;
Figure 3 illustrates in Figure 3A and in Figure 3B partially schematic side and end
elevational views respectively illustrating the vacuum locks intermediate a corresponding
plasma reactor and the R, TT movable arm assembly of the multiple-processing and contamination-free
plasma etching system according to the present invention;
Figure 4 is a partially pictorial and partially sectional view useful in explaining
the operation of the R, TT movable wafer arm assembly of the multiple-processing and
contamination-free plasma etching system according to the present invention;
Figure 5 is a perspective view of a first embodiment of R, TT movable wafer arm assembly
of the multiple-processing and contamination-free plasma etching system according
to the present invention;
Figures 6 and 7 are plan views of the first embodiment of the R, TT movable wafer
arm assembly illustrating different movement positions of the R, TT movable wafer
arm assembly of the multiple-processing and contamination-free plasma etching system
of the present invention;
Figure 8 is a partially broken-away and fragmentary isometric view illustrating a
portion of the first embodiment of the R, TT movable arm assembly of the multiple-processing
and contamination-free plasma etching system of the present invention;
Figure 9 is a partially pictorial and partially schematic side view illustrating a
plasma reactor of the multiple-processing and contamination-free plasma etching system
according to the present invention;
Figure 10 is a diagramatic view illustrating the several reactant injection systems
and controlled vacuum system of the multiple-processing and contamination-free plasma
etching system of the present invention;
Figure 11A is a perspective view and Figure 11B is a sectional view of a second embodiment
of the R, TT movable arm assembly of the multiple-processing and contamination-free
plasma etching system of the present invention;
Figure 12 is a perspective view of a portion of the second embodiment of the R, TT
movable wafer arm assembly of the multiple-processing and contamination-free plasma
etching system according to the present invention; and
Figures 13-18 are SEM micrographs illustrating exemplary microstructures obtainable
by the multiple-processing and contamination-free plasma etching system according
to the present invention.
Figure 19 is a system level state diagram describing system initialization and cassette
insertion and extraction states;
Figure 20 is a state diagram identifying states associated with system processing
of wafers and individual wafer processing instructions;
Figure 21 is a state diagram identifying states in sequencing a wafer from one plasma
etch vessel or chamber to another;
Figure 22 is a state diagram identifying wafer transport from a vessel or chamber
to its cassette slot;
Figure 23 is a state diagram identifying wafer transport from a cassette slot to a
vessel or chamber;
Figure 24 is a state diagram identifying the wafer processing within an individual
plasma etch vessel or chamber.
[0006] Referring now to Figure 1, generally designated at 10 is a pictorial diagram illustrating
the multiple-processing and contamination-free plasma etching system according to
the present invention. The system 10 includes a plurality of single-wafer plasma reactors
generally designated 12 to be described and a wafer queuing station generally designated
14 to be described that are arrayed about a closed locus as illustrated by a dashed
line 16. A load/unload module generally designated 18 to be described is disposed
concentrically within the plural plasma reactors 12 and the queuing station 14 for
singly transferring wafers to be processed and after processing between the queuing
station 14 and one or more of the plasma reactors 12. A plurality of vacuum locks
generally designated 20 to be described are individually provided at the interfaces
of the several plasma reactors 12 and the load and unload module 18, and between the
interface of the queuing station 14 and the load and unload module 18. A processor
22 is operatively coupled to the plural plasma reactors 12, to the queuing station
14, and to the load and unload module 18 for activating and de-energizing radio frequency
plasma inducing fields in well-known manner, for controlling and processing in well-known
manner the signal output of end-point determination means coupled to the several plasma
reactors, and for initiating and coordinating wafer transfer between the several reactors
and the queuing station to be described.
[0007] A reactant gas injection system 24 to be described is operatively coupled to the
plural plasma reactors 12 for controllably injecting preselected reactants and other
process gases severally into the plural plasma reactors. A vacuum system 26 is operatively
coupled to the reactors 12, to the queuing station 14, and to the load and unload
module 18 for maintaining the entire assembly at a controlled vacuum condition during
operation. The process 22 is operatively coupled to the reactant gas injection system
and to the vacuum system 26.
[0008] The several reactors 12, the queuing station 14, and the concentric load and unload
module 18 conserve space utilization and in such a way as to provide a comparatively-compact
plasma etching system. The load and unload module 18 and cooperative ones of the vacuum
locks 20 are operable to transfer wafers singly between the queuing station 14 and
selected reactors 12 in a single-step processing mode and between selected reactors
12 in a two or more step processing mode without any residual or environmentally-induced
wafer contamination as well as without intermediate operator handling. Among other
additional advantages, the plasma etching system of the present invention is characterized
by both an excellent process control and a high processing throughput, the mutual
coexistence of both features having not heretofore been possible in a practicable
embodiment.
[0009] Referring now to Figure 2, generally designated at 30 is a fragmentary plan view,
partially broken-away, illustrating the multiple-processing and contamination-free
plasma etching system of the present invention. The queuing station 14 preferably
includes a cassette, not shown, having plural vertically-spaced wafers 32 stacked
therein. The cassette is preferably mounted for vertical stepping motion by an indexed
elevator assembly schematically illustrated at 34, that is operable under control
of the processor 22 (Figure 1) to step the cassette in vertical increments that correspond
to the spacing of the vertically spaced wafers for addressing the associated cassette
slot position. It will be appreciated that in this way individual wafers in the cassette
are addressed for removal for processing and for return after processing to their
corresponding slot positions. It should be noted that although a cassette and indexed
elevator assembly are presently preferred, any other suitable wafer queuing station
can be employed as well without departing from the inventive concept.
[0010] Referring now to Figures 2, 3A and 3B, the vacuum locks 20 intermediate the queuing
station 14 and the load/unload module 18 and intermediate the plural plasma reactors
12 and the load and unload station 18 each include a housing body generally designated
40. The housing 40 includes a plate 42 having opposing top, bottom, and side walls
44 orthogonal thereto that cooperate to define a generally-rectangular hollow generally
designated 46 therewithin as best seen in Figure 3A. A flange 47 is provided peripherally
around the walls 44 on the ends thereof remote from the plate 42, and bolts 48 are
provided through the ends of the plate 42 and of the flange 47 for fastening the housing
body 40 at the interfaces between corresponding ones of the plasma reactors 12 and
the load and unload station 18 and between the interface between the queuing station
14 and the load and unload station 18. O-rings 50 are provided on the sealing faces
of the plate 42 and flange 47 for providing an air-tight seal. An elongated slot generally
designated 54 is provided through the plate 47 that is in communication with the generally-rectangular
hollow 46.
[0011] A chamber door assembly generally designated 56 is cooperative with the slot 54 to
provide a valving action. The door assembly 56 includes an elongated, generally-rectangular
plate 58 of dimensions selected to be larger than the dimensions of the slot 54. An
O-ring sealing member 60 is provided in the sealing face of the plate 58 and surrounding
the slot 54. The plate 58 is fastened to an arm 62 that is mounted for rotary motion
with a shaft 64 journaled in spaced bearings 66 that are fastened to the plate 42.
A chamber door TT-drive actuator, not shown, is fastened to the shaft 64 through the
edge of the housing 40 preferably via a ferrofluidic or other rotary seal as illustrated
dashed at 70.
[0012] The chamber door 56 is pivoted by the chamber door TT-drive actuator between an open
condition, illustrated in dashed outline in Figures 3A, and a closed condition, illustrated
in solid outline in Figures 3A and 3B. In its open condition, the generally rectangular
hollow 46 is in open communication with the elongated slot 54, so that a wafer arm
assembly to be described may readily be moved therethrough between the load and unload
station 18 and the several plasma reactors 12 and the queuing station 14. In the closed
condition of the door assembly 56, the load and unload module is sealed from the plural
plasma reactors 12 and from the queuing station 18.
[0013] Referring now to Figures 2 and 4, the load and unload module 18 includes a top wall
72, pentagonally-arranged side walls 74, and a pentagonal bottom wall 76 defining
an enclosure generally designated 78. A R, TT movable wafer arm assembly generally
designated 80 to be described is mounted in the enclosure 78. The assembly 80 includes
a turntable 82 mounted for TT-rotation with a shaft 84 journaled in a bearing assembly
generally designated 86 that is fastened in a central aperture provided therefor in
the bottom wall 76. A Theta drive motor 88 mounted to the bottom wall 76 is operatively
coupled to the shaft 84 via a belt and wheel arrangement generally designated 90.
With controlled rotation of the shaft of the Theta-motor 88, the shaft 84 and therewith
the turntable 82 rotates to any selected angular TT orientation for aligning the wafer
arm assembly 80 with any one of the plasma reactors 12 or with the queuing station
14 at the corresponding TT₁, TT₂, TT₃, TT₄, and TT₅ coordinates.
[0014] A shaft 92 is concentrically mounted within the shaft 84 and journaled for rotation
therein on a bearing and vacuum seal assembly generally designated 93. Any suitable
rotary vacuum seal, such as a ferrofluidic rotary vacuum seal, may be employed. On
end of the shaft 92 is connected to pivot bearing 94 to be described vacuum-mounted
through the turntable 82, and the other end of the shaft 92 is operatively coupled
to a R-drive motor 92 via a belt and wheel arrangement generally designated 98. As
described more fully below, with the controlled rotation of the shaft of the R-drive
motor 96, the wafer arm of both embodiments of the R, TT movable wafer arm assembly
to be described is controllably translated in the R-direction for loading and unloading
idividual wafers into and out of the plural reaction chambers 12 and queuing station
14 through the associated vacuum lock 20.
[0015] Referring now to Figures 2, 4, and 5, th wafer arm assembly 80 includes a wafer receiving
and releasing paddle assembly generally designated 100. The paddle assembly 100 includes
a platform 102 having a central opening generally designated 104 therethrough. The
member 102 terminated in laterally spaced fingers 106 having wafer-periphery engaging
upstanding flanges 108 integrally formed on the free ends thereof. A releasable abutment
generally designated 110 having a bumper portion 112 and an integral tail portion
114 is mounted for sliding motion to the platform member 102. As best seen in Figure
8, a coil spring 116 is mounted between the releasable abutment 110 and the member
102 which urges the bumper 112 in the direction of an arrow 118 so as to abut and
therewith frictionally engage the periphery of a wafer, not shown, received between
the bumper 112 and the flanges 108. The tail 114 includes a downwardly depending stop
120 to be described that is slidably received in an elongated aperture provided therfor
in the platform member 102 that is cooperative with an upstanding abutment to be described
to release the frictional wafer engagement as the arm reaches its position of maximum
extension. The paddle assembly 100 is mounted between plates 124 to a carriage assembly
generally designated 126 that is slidable mounted on linear bearings 128 that are
fastened to end posts 130 upstanding from and fastened to the rotatable turntable
82.
[0016] The carriage 126 is controllably moved in either direction along the linear bearings
128 for loading and unloading wafers individually to and from the several plasma reactors
12 and the queuing station 18. A member 131 is pivotally mounted subjacent the carriage
126, which houses therein a linear bearing, not shown. A shaft 132 is slidably received
through the linear bearing of the pivoting housing 131. One end of the shaft 132 is
slidably mounted in a sleeve 134 that is mounted for rotary motion to the turntable
82 via a pivot bearing 136, and the other end of the shaft 132 is fastened to a needle
bearing assembly 138 that is pivotally fastened to a crank arm 140 mounted for rotation
with the shaft 92 of the R-drive motor 96 (Figure 4) via a mounting coupling 142 fastened
to the turntable 82.
[0017] With controlled rotation of the Theta-drive motor 88, the turntable 82 and therewith
the paddle assembly 100 is rotated to that TT coordinate that corresponds to any selected
one of the angular locations of the plural plasma reaction chambers designated TT1
through TT4 in Figure 2, and to that TT coordinate that corresponds to the angular
location of the wafer queuing station 14 designated TT5 in Figure 2. With the controlled
rotation of the R-drive motor 96, the crank 140 traces an arcuate path as illustrated
by an arrow 144. The arm 132 therewith pivots on the pivot bearing 136 as shown by
an arrow 146, and moves the carriage 126 linearly along the bearings 128 in a direction
that corresponds to the sense of rotation of the X-drive motor as illustrated by an
arrow 148. The arm is either more or less elongated relative to the coupling 136 as
it is pivoted by the crank 140, and depending on the sense of the rotation, it slides
within the sleeve 134 and within the housing 131 as illustrated by an arrow 150. When
the crank 140 is turned to its maximum clockwise position, the paddle assembly 100
moves into its fully retracted position as illustrated generally at 152 in Figure
6. With counterclockwise motion of the crank arm 140 the paddle moves along the R
direction as illustrated generally at 154 in Figure 7. As the paddle assembly 100
nears its fully extended position, close to the maximum allowed counterclockwise rotation
of the R-drive motor, the stop 120 on the tail portion 110 abuts the confronting wall
of the upstanding end post 130, such that with continued motion of the paddle along
the R direction the bumper 110 draws away from the flanges 108 and thereby releases
the frictional engagement of the wafer periphery. In the maximum extended position,
then, the wafers are free to be loaded or unloaded to and from any selected plasma
reactor 12 and/or are free for pick up or delivery back into the queuing station 14.
[0018] Contacts 156, preferably three in number, are mounted to the platform member 102
of the paddle assembly 100 as shown in Figure 7. The contacts are operative in response
to the presence of a supported wafer to provide a three-point signal indicative of
whether or not the wafer is properly seated on the wafer transfer arm. The contacts
preferably are formed on a printed circuit board, not shown, mounted to the paddle
assembly 100. A different number thereof, or other sensing means may be utilized,
so long as an accurate indication of intended seating of individual wafers is provided.
[0019] Referring now to Figure 9, generally designated at 160 is a partially pictorial and
partially schematic side view illustrating a plasma reactor of the multiple-processing
and contamination-free plasma etching system according to the present invention. Each
of the plasma reactors 160 includes a top plate 162, a spaced-apart bottom plate 164
and a cylindrical sidewall 166 cooperate to define a plasma chamber generally designated
168. A first electrode generally designated 170 is fastened to the bottom plate 164.
A pedestal schematically illustrated dashed at 172 is slidably mounted centrally in
the bottom electrode 170 for vertical motion with the shaft of a pneumatic cylinder
schematically illustrated in dashed outline 174. As described more fully below, the
pedestal 172 is cooperative with the paddle arm assembly to allow for removal and
delivery of individual wafers into and out of the plasma chambers. The pedestal pneumatic
cylinder 174 is driven by a controlled air supply, now shown, operatively coupled
thereto via an air input port 176 and an air output port 178. As illustrated by dashed
outline 180, a source of colling liquid, not shown, is coupled to internal fluid flow
passageways, not shown, provided through the interior of the bottom electrode 170
via input and output ports 182, 184 for removing the heat produced in the bottom electrode
during plasma etching. A top electrode generally designated 186 is fastened to a support
shaft generally designated 188 that is slidably received through the top plate 162
in a vacuum-tight sealing engagement therewith as by a stainless steel vacuum bellows
190 fastened between the top plate 162 and a superadjacent shaft support plate 187.
The top electrode 186 includes internal cooling/heating fluid flow passageways schematically
illustrated in dashed outline 189 that are coupled via fluid flows conduits 190 disposed
in the shaft 188 to a source, not shown, via a liquid input port 194 and an output
port 196 provided in the plate assembly 187. A pneumatic actuator generally designated
200 having a ram 202 is mounted to the support plate assembly 187. With the ram 202
in its extended position, not shown, the plate 187 moves upwardly, and therewith the
shaft 188 and electrode 186 move upwardly and away from the stationary bottom electrode
170. With the ram lowered as shown, micrometer adjustment posts 204 fastened to the
plate assembly 187 bear against the top plate 162 and therewith support the top electrode
186 in an intended spaced-apart relation with the bottom electrode 170. The gap between
the electrodes is adjustable by changing the length of the micrometer adjustment posts
selectively. In the preferred embodiment, between 2/16 inch to 2 inches of gap adjustment
is provided.
[0020] The shaft 188 has a hollow interior generally designated 206, and a laser window
208 is mounted across the hollow of the shaft 206. The beam of an external laser,
not shown, passes through the window and hollow shaft for providing end-point determinations
of the plasma etch state. Other end-point determination means, such as a lateral optical
detector, may be employed as well without departing from the inventive concept. Reactant
gas injection ports 210 are coupled via internal shaft conduits provided therefor,
not shown, to a liquid-cooled showerhead gas manifold illustrated in dashed outline
211 in the upper electrode 186. Reactant gas is controllably released therefrom into
the plasma reactor, and radio frequency power is applied in the plasma reaction chambers.
In an alternative embodiment, the spacing between the electrodes can be preselected
for each particular plasma process, and additional micrometers, in place of the pneumatic
actuators 200, can advantageously be employed.
[0021] Referring now to Figure 10, generally designated at 212 is a schematic diagram illustrating
the presently preferred gas injection and controlled vacuum systems. Preferably, four
independently valved sources of gases are respectively connected to individual ones
of plasma vessels via corresponding ones of a plurality of gas manifolds, two banks
of gas sources generally designated 214, 216 and two manifolds 218, 220 being specifically
illustrated. A vacuum system 22 is operatively coupled in common to the plural plasma
reactor chambers, to the queuing stations 224, and to the load and unload island 226.
The vacuum system controls the vacuum condition in the entire system, so that the
wafers are free from possible contamination as the vacuum locks are severally opened
and closed during single and multiple phase processing wafer transfer. It should be
noted that while four plasma reactors are disclosed, a greater or a lesser number
can be employed without departing from the inventive concept.
[0022] Referring now to Figure 11A, generally designated at 230 is a perspective view of
an alternative embodiment of the X. TT wafer arm assembly according to the present
invention. The assembly 230 includes a pully 232 mounted for rotation with the shaft
of the TT drive motor as best seen in Figure 11B. The pulley 232 includes a grooved
rim 234 around which a cable 236 is wrapped. The cable is drawn tangentally to the
grooved rib 234 in opposing directions, and respectively wrapped over pulleys 238,
240 and tied to a slide 242, as best seen at 244 in Figure 11B. With the angular rotation
of the pulley 232, the slide 242 linearly moves along the linear bearings 246. A wafer
arm generally designated 248 is mounted for movement with the slide 242 such that
the arm 248 is controllably extended and retracted in dependence on the angular position
of the pulley 232. To provide constant-tension in the cable 236, the ends of the cable
preferably are terminated in the slide 242 against resilient biasing elements generally
designated 250 in Figure 12. The cable 236 as it stretches is pulled in a reverse
direction by the resilient couplings 250 for maintaining its intended state.
[0023] During the plasma chamber load cycles, the Theta-drive motor turns the turntable
of the R, TT wafer arm assembly to the TT coordinate of the queuing station in either
embodiment of the R, TT movable wafer arm assembly. The vacuum lock of the associated
interface is released, and the arm is extended under the wafer in the addressed cassette
slot position. The arm is then retracted back into the load and unload module, and
the vacuum lock is restored. The R, TT wafer arm assembly is then rotated to the TT
coordinate of the selected plasma reactor. The associated chamber door is then rotated
to its open condition for providing access to the selected reaction chamber, and the
upper electrode is raised. The wafer receiving arm is then extended in the R direction
through the associated slot valve opening and into the selected reaction chamber.
As it approaches the limit of its maximum radial travel, the depending stop flange
on the wafer arm abuts the upstanding end post on the turntable and, with continued
radial motion, the bumper withdraws thereby freeing the wafer from peripheral friction
engagement. The central pedestal of the lower electrode is then controllably raised
by its pneumatic actuator, and therewith the wafer supported on the arm is elevated
upwardly off of the wafer support platform. Thereafter, the wafer arm is retracted
out of the plasma chamber through the open slot valve and back into the load and unload
station. The pedestal is then controllably lowered. The wafer lowers therewith until
the pedestal is in its retracted position and the wafer is supported on the surface
of the lower electrode. The associated chamber door is then closed, and the upper
electrode is lowered to that precise preselected gap that implements the particular
plasma process being run. The intended reactants are then injected through the gas
manifold of the upper electrode, the radio frequency power is applied. Whereupon,
plasma etching of each single wafer is continued until the laser provides a signal
indication that the proper end-point has been achieved. Thereafter, the RF power is
turned-off, the vacuum lock is opended, and the above-described process is repeated,
but in reverse order, for removing the wafer out of that plasma chamber and back into
the load and unload station. The wafer can then be moved into another plasma reactor
for a subsequent process in a two or more step processing mode, or back into the cassette
in a one-step processing mode.
[0024] The load and unload module, queuing station, and plural reactors are operable in
three basic modes, namely, where each reactor is simultaneously performing the same
plasma reaction, where each plasma reactor is simultaneously performing two or more
different plasma processes, and where the plasma reactors are severally being operated
to provide multiple-step processing of single wafers before their return back to the
queuing station. In each case, the wafers are transferred and processed in a controlled
vacuum environment such that atmospheric exposure and handling induced contamination
are wholly eliminated.
[0025] Figure 13-17 are scanning electron micrographs illustrating exemplary microstructures
capable of being formed in a single-step process, and Figure 18 is a scanning electron
micrograph illustrating an exemplary microstructure capable of being fabricated in
a double-step etch process. Figure 13 shows generally at 260 polysilicon with an overlayed
photoresist 262 on the surface of the silicon dioxide layer 264 of the wafer. For
exemplary low-resistivity (12-13 ohms) doped polysilicon, CCl₄ at 20 sccm and H
e at 30 sccm are applied to the plasma reactor at a pressure of 100 mt and a power
of 300 watts. The etch occurs for approximately 1 1/2 minutes. As shown in Figure
14 doped polysilicon 265 having a comparatively high resistivity (30-200 ohms per
sq.) and having a slopped profile mask is illustrated. For the illustrated microstructure,
SF₆ at 50 sccm and freon 115 (C₂CIF₅) at 50 sccm are controllably injected into a
plasma reactor at 150 mt pressure and a 100 watt power. After about 2 1/2 minutes,
the illustrated doped polysilicon microstructure is fabricated.
[0026] Referring now to Figure 15, generally designated at 266 is a SEM illustrating an
exemplary trench etc. The photoresist is removed, and a trench generally designated
268 is formed in the silicon 272 by injecting BCl₃ at 5 sccm and Cl₂ at 25 sccm into
the plasma reactor at a 100 mt chamber pressure and at 750 watts power for about 20
minutes.
[0027] Referring now to Figure 16, refractory silcide, TaSi/poly, is illustrated generalldy
at 274. The silicon dioxide surface 276 is overlayed with a polysilicon layer 278
upon which is overlayed the TaSi/poly 280 over which is the photoresist. The microstructure
is fabricated by injecting CCl₄ at 20 sccm and He at 30 sccm into a plasma reactor
maintained at a chamber pressure of 80 mt and a radio frequency power of 300 watts
for about 3 1/2 minutes.
[0028] Referring now to Figure 17, generally designated 282 is another microstructure exemplary
of the single-step structures capable of being fabricated by the contamination-free
and multiple-processing plasma reactor of the present invention. As illustrated, a
photoresist 284 is layed over an aluminum and silicon layer 286 which is overlayed
via a TiW layer 288 on the wafer surface. The illustrated structure was fabricated
by injecting BCl₃ at 50 sccm with Cl₂ at 15 sccm into the plasma reactor maintained
at 125 mt chamber pressure and a 300 watt RF power for about 2 1/2 to 3 1/2 minutes.
[0029] Referring now to Figure 18, generally designated at 290 is a silicon dioxide/poly/silicon
dioxide/poly sandwich structure illustrating an exemplary two-step process. A poly
layer designated poly 1 and an oxide layer designed oxide are formed after etching
with C₂F₆ at 100 sccm at a 700 mt pressure and a 600 watt radio frequency power in
a first chamber. Thereafter, the upper poly 2 layer and the oxide and an overlayed
photoresist layer are formed by a separate step employing CCl₄ at 20 sccm and He at
30 sccm in a second reaction chamber maintained at a 100 militore chamber pressure
and a 600 watt radio frequency power.
[0030] With respect now to Figs. 19-24, the processor control for wafer throughput is illustrated.
In particular, Fig. 19 illustrates a state diagram for overall system operation. In
the state 300, system initialization procedures are accomplished which take the system
from a turn-on state through necessary warm-ups and start up proceedures. Transition
to a subsequent state 302 occurs once the system initialization has been completed.
State 302 exists until a cassette has been placed into the cassette queue station
and all door interlock switches are activated. The transition from the determine ready
state 302 to a machine initialization state 304 occurs once these conditions have
been met and the operator initiates system operation through a start button, provided
no other system interrupt signals or hold designations have occurred and provided
the user has not activated the diagnostic state 306 which is alternatively entered
from the determine ready state 302.
[0031] The diagnostic state 306 runs a set of diagnostics on the system should that state
be entered by the user. Otherwise, the machine initialization state 304 accomplishes
a final set of system power-ons, gas perge or other initialization steps which would
not normally be entered in the system initialization state 300 for time and/or power
considerations.
[0032] From the machine initialization state 304 a standby state 306 may be entered by operator
designation through a standby button which effectively aborts the processing steps
back to the determine ready state 302. Otherwise, from the machine initialization
state 304, once the initialization functions have been completed, the system transitions
to a cassette pump down state 310 in which a vacuum is drawn from the wafer queuing
station 14 placing it into the environment of the transport arm and plural etch vessels.
After pump down of the wafer queuing station 14, state 310 processing will normally
transition to the state 312 in which the wafers and the cassette at the queuing station
14 are processed in sequence as illustrated in the subsequent figures. Alternatively,
if in the determine ready state 302 the operator had activated a clear wafer instruction,
processing would transition to a clear wafer state 314 in which, in liew of cassette
processing, wafers are cleared from the system. In the case of each state 306, 308,
and 314 processing, after completion of their state functions, will return to the
determine ready state 302.
[0033] If the cassette processing state 312 is entered, the system processes each wafer
in the cassette according to a wafer command list entered into the system and described
below. Once that cycle is complete, processing proceeds to a state 316 which vents
the wafer queuing station 14 and waits until removal of the cassette at which point
the system transitions to state 300.
[0034] Should any error occur in normal system operation, as determined by processor error
detection, processing from each of the states of Fig. 19 will return to the system
initialization state 300 to rerun the power-on initialization functions.
[0035] The operation within the cassette process state 312 follows a flexible processes
control illustrated in the flow diagram of Figure 20. As illustrated there processing
proceeds between state 320 labeled slots, state 322 labeled wafers, state 324 labeled
wafer commands, and state 326 labeled machine monitors. The processing of Figure 20
is initiated when the state 312 is entered with a cassette of unprocessed wafers,
and starts, and finishes, in state 320. State 320 initiates a wafer start command
for each slot containing an unprocessed wafer using, for example, a top to bottom
priority scheme, or any other priority scheme which may be programmed. From the state
320 for a selected slot, and corresponding wafer, processing proceeds to the wafer
state 322. From state 322 the processing commands or specifications for each wafer
are accessed in a subsequent state 324, wafer commands. The wafer commands will be
programmed into the system corresponding to the desired processing of each wafer,
for example, one or more etches for a designated time period or depth in a designated
gas. The commands in the state 324 are executed in sequence, and each command commences
a set of machine control operations which occur in state 326, machine monitors.
[0036] At the completion of each wafer command, representing for example, a single etch
cycle for a wafer as described below, processing returns to the wafer command state
324 to execute another wafer command. After all wafer commands have been executed
for a particular wafer, processing returns to the state 322 and from thence to state
320 thereby sequencing through the wafers and the cassette slots.
[0037] Processing within the machine control state 326 is in accordance with the wafer transport
algorithms of Figs. 21, 22 and 23 and the internal chamber or vessel processing algorithm
of Fig. 24. In each case where processing halts for receipt of system instructions
to proceed, processor state evaluation checks for existence conditions necessary for
the unit to proceed to the next step.
[0038] With particular regard to Fig. 21 illustrates processing for moving a wafer from
one chamber or vessel to another, in accordance with wafer commands specifying multiple
chamber or vessel processing. As shown there processing commences at initialization
state 330. Subsequent state 332 directs the transport arm wafer support table from
one chamber or vessel to the desired chamber or vessel wherein the wafer to be moved
is located. Once that positioning is accomplished a subsequent state 334 activates
the valve and arm mechanisms in a transition to a state 336. In state 336 the system
repositions the transport arm wafer support table to the destination chamber or vessel
and transitions to a state 338 which, when it receives control signals, activates
the arm mechanism and valving on the applicable chamber to place the wafer in that
particular chamber in the transition to a state 340. When state 340 is reached, the
wafer relocation function is complete and processing returns to the next wafer command
in state 324.
[0039] Fig. 22 illustrates the processing wherein a wafer is moved from a chamber or etch
vessel to a slot of the cassette. From an initialization state 350 processing transitions
to a state 352 which awaits the direction of the transport arm wafer support table
to the desired chamber having the wafer to be returned to the cassette. Once the proper
positioning is accomplished, the transition from state 352 to state 354 sends a request
to the command list asking to be instructed to remove the wafer from the chamber.
When that instruction is received in state 354, the transition to state 356 executes
the machine instruction to open the valves and move the transport arm to pick up the
wafer in the chamber and extract it from the chamber or vessel and in addition to
request from the wafer command list the instructions to move to the cassette. When
those instructions are executed and the arm is positioned to apply a wafer to the
cassette, the system transitions to state 358 and sends a request to the wafer processing
list for instructions to place the wafer into the cassette and identified slot. When
that information is received the transition to the done state 360 executes the wafer
insertion into the cassettes slot and returns processing back to the algorithm of
Fig. 20.
[0040] Fig. 23 illustrates the algorithm for transferring a wafer from the cassette to a
designated chamber in accordance with instructions in the wafer command list. From
an initialize state 370, processing transitions to a state 372 in which the request
is sent to the command list for instructions to position the arm to the cassette and
such arm manipulation is executed. When the arm is appropriately positioned in state
372, the system transitions to state 374 in which a request for the instructions to
extract a wafer from the cassette is sent. The state 374 has two possible outcomes,
in the first represented by branch 376, a wafer is not found in the slot in which
the system has been instructed to retrieve it by the transport arm. In this case the
system transitions to a done state 378 indicating that the algorithm of Fig. 23 has
progressed as far as it can, albeit in an abort condition. In the other possible outcome
of state 374, the wafer is found and the system transitions from state 374 to state
380 in which instructions are received from the wafer processing list to position
the transport arm support table at the destination chamber or vessel. When, in state
380, that destination chamber is reached, the system transitions to a state 382 in
which the system requests and receives instructions from the command list (if the
chamber is ready) to insert that wafer into the chamber. In the transition from state
382 to the completed state 378, the mechanisms of the arm and the chamber valving
are activated in order to install the wafer into the chamber.
[0041] Fig. 24 illustrates the processing of the system for accomplishing wafer etching
within a chamber to which the system has allocated a wafer from the cassette at the
queuing station.
[0042] The processing of Fig. 24 is initiated by a start command obtained from the command
list which initiates a state 390. The state 390 loops through an error recognition
state 392 to a start command wait step 394 if the start command is determined to have
incorrect signature. Otherwise, processing from a state 390 proceeds to a state 392
in which the valve to the chamber is sealed and the electrode spacing set to the etch
condition. A subsequent step 394 waits for confirmation signals from microswitches
indicating proper gate closure and electrode positioning. Subsequently a state 396
commences the flow of a gas, selected from the wafer command list, for the desired
processing and waits for a steady state gas condition, based on time or other factors,
to occur. Subsequently a transition to a state 398 activates the RF plasma generation
between the electrodes used for plasma etching within the gas and wafer processing
by gas vapor etch continues until a parameter indicating complete processing is obtained.
Such a parameter may be a function of time, detected etch depth, or other factors.
Once wafer processing is indicated as complete, the transition from state 398 to state
400 deactivates the RF and in state 400 the gas environment in the chamber is evacuated
so that, in subsequent state 402, the electrodes can be respaced for wafer removal,
and the gate or chamber doors opened to the environment of the transport arm without
fear of leaking reactor gas into that environment. State 402 transitions to state
404 in which the system awaits confirmation by microswitch activation of proper electrode
spacing and opening and transitions to state 394 in which system processing returns
to the flexible process control of Fig. 20.
1. A multiple-processing and contamination-free plasma etching system, characterized
by plural, single-wafer plasma etching vessels each having an ingress and egress defining
port that are arrayed about a predetermined spacial locus in such a way that the several
ports thereof are accessible from a single location spaced from the several ports,
a wafer queuing station spaced with the plural vessels along the same predetermined
spacial locus defining a wafer access port accessible from said single location, plural
valve means individually coupled to corresponding ones of said plural, single-wafer
plasma etching vessel ingress and egress ports and to said wafer queuing station wafer
access port, single-wafer transfer means disposed at said single location and cooperative
with corresponding ones of said plural valve means for moving wafers from and to said
wafer access port of said queuing station from and to selected ones of said single-wafer
plasma etching vessels through the associated one of said ingress and egress ports
thereof, and processor means for controlling said vessels, said transfer means and
said valve means to provide selectable single or multistep processing of wafers in
said queuing station in one or more of said etching vessels.
2. A system according to claim 1, characterized in that said predetermined spacial
locus is a closed locus, and wherein said single location coincides with the geometric
center of said closed locus.
3. A system according to claim 1, characterized in that each of said plural plasma
etching vessels include walls defining a plasma chamber, in that each of said plural
plasma etching vessels further include first and second electrodes, and means for
mounting said first and said second electrodes to said walls for relative electrode
motion, and in that each of said plural plasma etching vessels further include means
for cooling/heating said first and said second electrodes thereof.
4. A system according to claim 1, characterized in that said wafer transfer means
includes a wafer receiving arm, and means mounted to the arm for picking-up single
wafers by contacting their periphery and in such a way that no contact is made of
the front surface of the wafer.
5. A system according to claim 2, characterized in that said wafer transfer means
includes an R, TT moveable wafer receiving arm having means for picking-up single
wafers disposed on said arm by contacting their periphery and in such a way that no
contact is made of the front surface of the wafers.
6. A system according to claim 5, characterized in that said R, TT moveable wafer
receiving arm assembly includes a base member platform and means for rotating said
base member platform in TT about an axis; a paddle; and means for mounting said paddle
for sliding motion in R relative to said base member platform.
7. A system according to claim 6, characterized in that said paddle includes a wafer
supporting first portion, a wafer edge engaging second portion, and means for mounting
said second portion for sliding motion relative to said first portion.
8. A system according to claim 7, characterized in that said first portion of said
paddle has an upstanding abutment on an edge thereof and wherein said wafer edge engaging
second portion includes a slide having a bumper that cooperates with said upstanding
abutment of said first portion to engage the periphery of a single wafer disposed
therebetween.
9. A system according to claim 1, characterized in that each of the plural single-wafer
plasma etching vessels includes a low-frequency plasma discharge producing source.
10. A system according to claim 1, characterized in that each of the plural single-wafer
plasma etching vessels includes a high-frequency plasma discharge producing source.
11. A system according to claim 1, characterized in that each of the plural single-wafer
plasma etching vessels includes a microwave-frequency plasma discharge producing source.
12. A system for providing semiconductor wafer etch processing of a plurality of semiconductor
wafers contained in a cassette in conjunction with a plurality of wafer etch chambers,
characterized by an array of wafer stations including at least one wafer cassette
queuing station adapted for containing a plurality of wafers in individual slots of
a wafer containment cassette, a plurality of wafer etch vessels, means for providing
gated entrance to said wafer etch vessels to provide in a first state sealed containment
of an environment within each of said vessels and in a second state access to the
vessel interior, means for transporting wafers between selected slots in a cassette
at said queuing station and the interior of selected plasma etched vessels via said
gated entrance means in said second state, processor means for sequencing wafers between
associated slot positions in a cassette of said queuing stations and one of more of
said plasma etch vessels in accordance with plasma processing commands associated
with each wafer.